Coburn Is Leaving the Senate at Year's End as He Battles Cancer

Republican Rep. James Lankford of Oklahoma on Monday became the first candidate to jump into the race to serve out the last two years of GOP Sen. Tom Coburn's term.

Mr. Coburn, who is battling a recurrence of cancer, said Thursday that he would leave the Senate when the current session of Congress concludes at year-end, two years before his second term ends. A primary for the seat will be held June 24, with a potential runoff Aug. 26,...